Inertia Sensors With Multi-Directional Shock Protection

ABSTRACT

A sensor including: a base; at least one component which moves relative to the base; and one or more locking mechanisms for locking the at least one component in a predetermined stationary position in response to external stimuli exceeding predetermined thresholds in at least first and second directions, where the first direction is different from the second direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/363,214 filed on Jul. 10, 2010, the entire contents of which isincorporated herein by reference.

GOVERNMENT RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of SBIR GrantNo. W15QKN-10-C-0068 awarded by the Department of Defense on Jun. 10,2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to sensors, and moreparticularly, to accelerometers and inertia based gyros that arehardened to multi-directional shock experienced during high-G (Gindicating the gravitational acceleration of around 9.8 m/sec²) firingsetback and set-forward.

2. Prior Art

The state of art in shock resistant accelerometer and inertia based gyrodesign is to reduce the size of the moving proof mass (gyroscopic proofmass for the case of inertia based gyros), thereby reducing the relatedforces, moments, and torques that are generated in the presence of highacceleration levels, i.e., when the accelerometer and gyro experiencesshock or impact loading. Hereinafter and for the sake of simplicity andsince the disclosed locking mechanisms apply equally to bothaccelerometers and inertia based gyros of various type, all such sensorsare referred to as accelerometers. In general stops are also provided inthe path of the moving component(s) of the accelerometer to limit itsmaximum deflection to protect such components from failure. Theintroduction of MEMS technology in recent years has made it possible toreduce the size of the proof mass significantly, independent of theaccelerometer type and its mechanism of operation. All existingaccelerometer designs, however, generally suffer from the followingoperational and/or performance deficiencies.

The most important shortcoming results from the reduction of the size ofthe proof mass since the sensitivity of an accelerometer is directlyrelated to the relative size of its proof mass, even if the shape anddesign of the accelerometer structure is optimally selected. As aresult, since highly accurate accelerometers are required for smartmunitions guidance and control during their flight (sometimesresolutions in 1/100 or even 1/1000 of one G) and other similarapplications, an accelerometer that can withstand tens of thousands ofone G with a floating proof mass cannot be designed to provide suchlevels of precision.

Another major shortcoming is related to the significant amount ofsettling time required for the accelerometer to settle within anacceptable level following shock loading. Many types of sensors,particularly accelerometers, rely upon the deflection of one or moreelastic structural elements of the sensor to make their sensorymeasurements. When subjected to firing setback or set-forward firingshock, which for a sensitive accelerometer or when the firingacceleration is high results in the proof mass to reach its travel limitat its (usually hard) stops, and generally impacting the stops. Thesensor is thereby “saturated” and the mechanical energy stored in thesensor components in the form of potential energy in the elasticelements and kinetic energy in the proof mass and other elements of thesensor will cause the sensor structure to begin to vibrate followingsuch impact events. The time until the vibration ceases or reduces to anacceptable value is referred to as a settling time. The settling time isparticularly important for accelerometers used in guns or similarlyfired projectiles and that are intended to be used for navigation and/orguidance and/or control purposes.

It is noted that accelerometers that are designed without proof masstravel limit stops and that can provide high sensitivity of theaforementioned order and that can tolerate high G shocks of the order oftens of thousands without permanent damage or change in theircharacteristics are yet to be conceived. This statement is also true foraccelerometers with proof mass travel limit stops when subjected to highG shocks of over 30,000-50,000 Gs. This is the case since due to thenature of all proof mass based accelerometers, high sensitivity to lowacceleration levels make them highly susceptible to shock loading damagesince they rely on relatively large deformations to be induced in theaccelerometer mechanism due to small input accelerations.

To alleviate the aforementioned shortcomings of proof mass basedaccelerometers and other similar inertia based sensors, active andpassive mechanisms are disclosed in U.S. Pat. No. 6,626,040 that areused to lock the proof mass (and potentially other moving elements ofthe sensor) to the base structure of the sensor, preferably at its nullposition or near its (currently experienced) acceleration level, whenthe accelerometer is subjected to a shock with acceleration levels abovea certain predetermined threshold. As a result, the proof mass and othermoving elements of the sensor are protected from impacting their stops(or other elements of the sensor or its packaging if no strops areprovided) and damaging the proof mass and/or other elements of thesensor. In addition, the generated dynamic forces acting on the proofmass and other elements of the sensor can better be distributed andsupported.

In the above patent, the inventors disclose different embodiments forproviding locking mechanisms for proof mass and other moving elements ofinertia based sensors (hereinafter, all such mechanisms are referred toas simply “locking mechanisms”), particularly for accelerometers. Theseembodiments may be divided into the following two basic classes oflocking mechanisms for proof mass and other moving elements of suchinertia based sensors:

1—Active type of locking mechanisms: In this class of lockingmechanisms, the means of actuating the locking elements is an activeelement such as an element that is powered electrically to generate amechanical displacement and/or rotation.

2—Passive type of locking mechanisms: In this class of lockingmechanisms, the means of actuating the locking elements is the dynamicforce and/or torque and/or bending moment that is generated by theacceleration experienced by the sensor when the acceleration level (forexample due to shock loading) reaches a predetermined level.

It is noted that in all the disclosed embodiments of the U.S. Pat. No.6,626,040 the locking action is achieved by providing mechanicalelements that would constrain the motion of one moving element relativeto another moving or fixed (generally meant to mean the structure of thesensor) element.

The aforementioned class of active type of locking mechanisms, includingthose embodiments that are disclosed in the U.S. Pat. No. 6,626,040, hascertain advantages over the aforementioned class of passive type oflocking mechanisms. They class of active type of locking mechanisms,however, suffer from shortcomings that make them unsuitable for a largenumber of applications, including those of guided gun-fired munitions,mortars, rockets and the like. The main advantages of the class ofactive type of locking mechanisms include the following:

1—The locking action may be initiated based on any sensory stimuli andsince certain electronics circuitry, logic and/or processing unit mustbe provided, a wide range of choices, including the use of certainalgorithms becomes possible for initiating the locking action. In fact,the locking action may be initiated even before certain event occurs oris timed to occur. As a result, this class of locking mechanismsprovides a high level of flexibility to the user.

2—When using the locking mechanism to protect the proof mass and othermoving elements of an inertia-based sensor (device) from shock loading,this class of locking mechanisms can provide the means to lock the proofmass and other moving elements of the sensor (device) irrespective ofthe direction of the shock loading. For example, when a round is firedby a gun, it is first subjected to firing (setback) acceleration insidethe barrel and then to an opposite set-forward acceleration, which eventhough is usually a fraction of the setback acceleration (usually around5-10 percent of the setback acceleration), but is still significantlyhigher than a desired threshold for locking the proof mass and othermoving elements of a sensor to protection against damaged. The use ofactive locking mechanisms in sensors such as accelerometers used ingun-fired munitions, mortars and the like provides the means to lock theproof mass and other moving elements of the sensor during both setbackand set-forward acceleration events.

The main shortcomings of the class of active type of locking mechanisms,including the shortcomings that make then unsuitable for most gun-firedmunitions, mortars, rockets and the like, include the following:

1—Active locking mechanisms require event detection components such assensors to detect the predetermined events, such a shock inducedacceleration threshold, to trigger the actuation of the lockingmechanism.

2—Active locking mechanisms require onboard electronics and/or logicscircuitry and/or processing units for event detection to initiate thelocking action or for timing such locking action initiation and toperform other related decision making activities.

3—Active locking mechanisms require actuation devices to operate. Suchactuation devices are usually powered electrically, and may be designedto operate using the principles of electrical motors or solenoids, oractive materials such as piezoelectric materials based elements.

4—In addition to requiring the aforementioned components to operate,active locking mechanisms also require electrical energy to power thesedevices. This requires the device using a sensor equipped with suchactive locking mechanism to be powered before an event that requireslocking mechanism activation could occur. For munitions and othersimilar applications, this requirement translates to a need for onboardpower sources to power sensor before launch. In addition, the totalamount of power that required for the operation of the sensor becomessignificantly higher than sensors equipped with passive lockingmechanisms. The said requirement of electrical power availability priorto firing and/or the significantly higher power requirement as comparedto sensors equipped with passive locking mechanisms make sensorsequipped with active locking mechanisms undesirable for gun-firedmunitions, mortars and the like applications.

5—In addition, devices using sensors equipped with locking mechanisms,particularly munitions, must also tolerate shock loading due toaccidental events such as, for example, drops from up to 7 feet overconcrete (hard) surfaces that can result in impact induced decelerationlevels of up to 2,000 G. This means that devices using sensors equippedwith active locking mechanisms cannot rely on their locking mechanismsto protect the proof mass and other moving elements of the sensoragainst such accidental drops since munitions cannot be powered at alltimes, even during assembly, transportation and storage. This in turnmeans that such sensors have to be provided with smaller proof mass toallow then to survive such accidental drops, i.e., their sensitivity hasto be limited to prevent being damaged during such accidental drops.

The embodiments of the class of passive type of locking mechanismsdisclosed in the U.S. Pat. No. 6,626,040, however, do not suffer fromthe above shortcomings of the class of active type of lockingmechanisms, including the embodiments disclosed in the said patent. Thesaid embodiments of class of passive type of locking mechanisms,however, suffer from the following shortcomings that make themundesirable for a large number of applications, including those ofguided gun-fired munitions, mortars, rockets and the like:

1—For gun-fired munitions, mortars and the like, the embodiments of theclass of passive type of locking mechanisms disclosed in the U.S. Pat.No. 6,626,040 provide protection to the proof mass and other movingcomponents of the sensor against shock loading generated by the firing(setback) acceleration only and not against the set-forward accelerationwhich is in the opposite direction to the setback acceleration.

2—Similarly, in case of accidental drops, the proof mass and othermoving components of the sensors are protected only if the deviceimpacts a hard surface in the direction causing sensor acceleration inthe direction of the firing setback acceleration. Otherwise if theimpact occurs on the opposite side of the device, i.e., if the impactinduced acceleration of the sensor is in the direction of theset-forward acceleration, then the proof mass and other movingcomponents of the sensors are no longer protected against the impactinduced shock.

The aforementioned class of passive locking mechanisms taught in theU.S. Pat. No. 6,626,040 and its aforementioned shortcomings are bestdescribed the embodiment of FIGS. 1 a and 1 b of the said patent.Referring now to FIGS. 1 a and 1 b, there is an accelerometer 100 shownschematically therein, which is intended to measure acceleration a inthe direction 101. The accelerometer consists of a proof mass 102 whichis rigidly attached to a relatively rigid base 106 (plate), a cantilever(bending) type of elastic element 103 with an equivalent spring rate kat the location of the proof mass 102 and in the direction of theacceleration 101. The proof mass 102 (with mass m) is located a distance104 (with length l) from the base 105 to which the elastic beam element103 is rigidly attached. In most MEMS types of accelerometers, thedisplacing plate 106 forms one side of a capacitor while the othercapacitor plate (not shown) is rigidly attached to the base 105. Thiscapacitor will then form the sensor that measures the elasticdisplacement of the proof mass due to the acceleration in the direction101.

The basic proof mass locking mechanism of this embodiment consists oflocking a first locking mass 108 which is attached to the base 105 byspring 107 on one side and locking a second locking mass 109 and spring110 on the opposite side of the proof mass base plate 106. The secondlocking mass 109 is attached to a lever arm 111, which is hinged to thebase 105 by the rotational joint 113. The spring 110 is attached to thebase 105 on one end and to the lever arm 111 on the other. Opposite tothe second locking mass 109 is positioned a moment mass 112 whichprovides a moment about the hinge joint 113 when the sensor isaccelerated in the direction of the arrow 101. The moment mass 112 has agreater mass than that provided by the first locking mass 109, therebyit tends to move the first locking mass 109 upwards due to theacceleration in the direction 101.

The spring rates of the springs 107 and 110 are selected such that atthe desired acceleration levels the gap between the first and secondlocking masses 109 and 108 and the plate 106 begin to close. A spacedlocking stop 114 is located along the plate 106 to lock the plate 106 atthe level dictated by the position of the locking stop 114. As a result,when the acceleration in the direction 101 reaches the selected level,the first and second locking masses 109 and 108 close the aforementionedgap, and thereby hold the base 106 and the proof mass 102 stationary atits null point, as shown in FIG. 1 b.

In general, the springs 107 and 110 are preferably preloaded, i.e.,provide a preset force in the direction of providing the required gapbetween themselves and the plate 106, and as the acceleration levelreaches the desired maximum level, they will begin to close the gap. Abasic mechanism to lock the proof mass 102 and/or other movingcomponents of an accelerometer is described above using an elastic beamtype of accelerometer. The design, however, can be seen to be applicableto almost all accelerometer and inertia based gyro designs, particularlythose constructed using MEMS technology, such as those employing alinear displacement, a ring type, and a torsional type of accelerometersor gyros.

The basic proof mass locking mechanism taught in the U.S. Pat. No.6,626,040, FIGS. 1 a and 1 b, is thereby seen to be capable of lockingthe proof mass to the base structure of the sensor when the shockacceleration experienced by the sensor is in the direction of the arrow101 but not in its opposite direction. For example, if the sensor isused in gun-fired munitions, the locking mechanism can be designed toprotect the sensor from the firing setback acceleration, but thegenerally significant set-forward acceleration of the said munitionsexperienced as the projectile exits the gun barrel can still damage thesensor. The sensor may similarly experience impact induced shockaccelerations from two opposite directions similar to setback andset-forwards accelerations due to accidental drops.

SUMMARY OF THE INVENTION

Thus, considering the aforementioned advantages of passive type oflocking mechanisms for inertia based sensors such as accelerometers, itis highly desirable to develop methods and means to provide such sensorwith passive type of locking mechanisms that lock the proof mass andother moving elements of the sensor when subjected to shock loading fromalmost any direction. For the particular case of inertia based sensorssuch as accelerometers to be used in guided gun-fired munitions,mortars, rockets and the like, it is highly desirable that passive typeof locking mechanisms be developed that could lock the proof mass andother moving parts of the sensor when it is subjected to both firingsetback acceleration as well as firing set-forward acceleration. Inertiabased sensors equipped with such passive type of locking mechanisms willhave all the advantages of the embodiments of the class of passive typeof locking mechanisms disclosed in the U.S. Pat. No. 6,626,040, but willnot suffer from their aforementioned shortcoming. The same lockingmechanisms may also be used to provide protection to inertia based gyrosof various types (such as those disclosed in U.S. Pat. Nos. 4,598,585 or5,203,208 or 5,488,862 or 6,009,751) by providing the means to lockinertia members and other moving elements of the gyro to the basestructure of the sensor when the experienced acceleration levels (bothlinear and rotational acceleration levels, such as those due to thefiring setback and set-forward acceleration levels and/or thosegenerated due to accidental drops) go beyond certain predeterminedthreshold. As a result, such gyros can be designed with larger (higherinertia) elements, thereby rendering them significantly more sensitiveand with significantly reduced settling time, while protected fromdamage due to accidental drops and for the case of gun-fired munitions,mortars, rockets and the like due to firing (setback) and set-forwardsaccelerations.

A need therefore exists in the art for sensors, in particularlyaccelerometers, which are sensitive enough to provide accurate sensingof a desired parameter, such as acceleration, yet rugged enough towithstand shock loading due to an external stimulus such as a high-Gaccelerations experienced by gun-fired munitions, mortars, rockets, andthe like during firing (setback acceleration), during set-forwardacceleration, and even during accidental drops over hard surfaces. Forthe particular case of gun-fired munitions, mortars, rockets, and thelike, i.e., for applications in which one or more of the aforementionedshortcomings of active types of locking mechanisms for the protection ofthe sensor proof mass and its moving components against shock loadingmakes then unsuitable, the provided locking mechanisms have to be ofpassive type.

A need therefore exists in the art for passive types of lockingmechanisms to protect proof mass and other moving elements of inertiabased sensors such as accelerometers and gyros against shock loadingfrom more than one direction to allow the sensors to be provided withsignificantly larger proof masses to significantly increase theirsensitivity. Furthermore, there is a need in the art for sensors, inparticularly accelerometers and gyros, in which the settling time of adeflected member is minimized.

Therefore it is an object to provide inertia based sensor with passivelocking mechanisms that would protect the sensor proof mass and othermoving elements against shock loading from multiple directions.

It is another object to provide the methods of developing such passivelocking mechanisms for inertia based sensors for protecting them againstshock loading from multiple directions.

In particular, it is an object to provide accelerometers and othersimilar inertia based sensors that are equipped with passive lockingmechanisms that would protects the sensor proof mass and other movingelements against shock loading from multiple directions, particularlyfor protecting such accelerometers and inertia based sensors used ingun-fired munitions, mortars and rockets from firing setbackacceleration as well as firing set-forward acceleration as well as shockloading due to accidental drops.

Accordingly, a sensor is provided. The sensor comprising: a base; atleast one component which moves relative to the base; and one or morelocking mechanisms for locking the at least one component in apredetermined stationary position in response to external stimuliexceeding predetermined thresholds in at least first and seconddirections, where the first direction is different from the seconddirection.

The sensor can be selected from a group consisting of an accelerometerand an inertial gyro. The external stimuli can be first and secondaccelerations of the sensor, the first acceleration being a setbackacceleration in the first direction and the second acceleration being aset forward acceleration in the second direction.

The at least one component can be a proof mass mounted to a deformablemember.

The one or more locking mechanisms can comprise a first sub-mechanismfor locking the at least one component in the predetermined stationaryposition in response to the external stimuli exceeding a firstpredetermined threshold in the first direction and a secondsub-mechanism for locking the at least one component in thepredetermined stationary position in response to the external stimulusexceeding a second predetermined threshold in the second direction.

The one or more locking mechanisms can comprise a single mechanism forlocking the at least one component in the predetermined stationaryposition in response to the external stimuli exceeding the predeterminedthresholds in both the first and second directions.

The one or more locking mechanisms can engage the at least one componentin rotation to lock the at least one component in the predeterminedstationary position.

The one or more locking mechanisms can engage the at least one componentin translation to lock the at least one component in the predeterminedstationary position.

The one or more locking mechanisms can be a first locking mechanism andthe sensor can further comprise a second locking mechanism for one oflocking or unlocking the first locking mechanism upon the occurrence ofa predetermined external stimulus.

At least one of the external stimuli can be a rotational acceleration.

Also provided is a sensor comprising: a base; at least one componentwhich moves relative to the base; and one or more locking means forlocking the at least one component in a predetermined stationaryposition in response to external stimuli exceeding predeterminedthresholds in at least first and second directions, where the firstdirection is different from the second direction.

Still further provided is a method for passively hardening a sensor fromexternal stimuli greater than predetermined thresholds. The methodcomprising: protecting one or more of a moving part and mechanism of thesensor from a first external stimulus in a first direction or minimizingresidual vibration of the one or more moving part and mechanism from thefirst stimulus in the first direction; and protecting the one or more ofa moving part and mechanism of the sensor from a second externalstimulus in a second direction or minimizing residual vibration of theone or more moving part and mechanism from the second stimulus in thesecond direction; wherein one or more of the first and second stimuli orfirst and second directions are different.

The protecting steps can comprise one or more of locking the one or moreof the moving part and mechanism to a base structure of the sensor orminimizing elastic deformation of the moving part and mechanism.

The external stimuli can be acceleration of the sensor and the firststimulus can be a setback acceleration in the first direction and thesecond stimulus can be a set forward acceleration in the seconddirection.

The protecting steps can be carried out by separate mechanisms. One ormore of the separate mechanisms can engage the moving part or mechanismin rotation to lock the moving part or mechanism in a predeterminedstationary position. One or more of the separate mechanisms can engagethe moving part or mechanism in translation to lock the moving part ormechanism in a predetermined stationary position.

The protecting steps can be carried out by a same mechanism. The samemechanism can engage the moving part or mechanism in rotation to lockthe moving part or mechanism in a predetermined stationary position. Thesame mechanism can engage the moving part or mechanism in translation tolock the moving part or mechanism in a predetermined stationaryposition.

The protecting steps can be carried out by one or more first mechanismsand the method can further comprise providing a second locking mechanismfor one of locking or unlocking the one or more of the first lockingmechanisms upon the occurrence of a predetermined external stimulus.

At least one of the first external stimulus and second external stimuluscan be a rotational acceleration.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus andmethods of the present invention will become better understood withregard to the following description, appended claims, and accompanyingdrawings where:

FIG. 1 a illustrates a schematic diagram of an accelerometer sensortaught in prior art having a passive means for locking the proof mass ina null position during periods of high acceleration in a singledirection.

FIG. 1 b illustrates the schematic of FIG. 1 a in which the proof massis locked in the null position.

FIG. 2 a illustrates a schematic diagram of an accelerometer sensorhaving a passive means for locking the proof mass in a null positionduring periods of up or down accelerations above a predeterminedthreshold.

FIG. 2 b illustrates the schematic of FIG. 2 a in which the proof massis locked in the null position.

FIG. 3 a illustrated the schematic of another accelerometer sensorembodiment of the present invention having a passive means for lockingthe proof mass in a null position during periods of up or downaccelerations above a predetermined threshold.

FIG. 3 b illustrates the schematic of FIG. 3 a in which the proof massis locked in the null position.

FIG. 4 a illustrated the schematic of another accelerometer sensorembodiment of the present invention having a passive means for lockingthe proof mass in a null position during periods of up or downaccelerations above a predetermined threshold.

FIG. 4 b illustrates the schematic of FIG. 4 a in which the proof massis locked in the null position.

FIG. 5 a illustrated the schematic of another accelerometer sensorembodiment of the present invention having a passive means for lockingthe proof mass in a null position during periods of up or downaccelerations above a predetermined threshold.

FIG. 5 b illustrates the schematic of FIG. 5 a in which the proof massis locked in the null position.

FIG. 6 a illustrated the schematic of another accelerometer sensorembodiment of the present invention having a passive means for lockingthe proof mass in a null position during periods of up or downaccelerations above a predetermined threshold.

FIG. 6 b illustrates the schematic of FIG. 6 a in which the proof massis locked in the null position.

FIG. 7 a illustrated the schematic of another accelerometer sensorembodiment of the present invention having a passive means for lockingthe proof mass in a null position during periods of up or downaccelerations above a predetermined threshold.

FIG. 7 b illustrates the schematic of FIG. 7 a in which the proof massis locked in the null position.

FIG. 8 illustrates the schematic of another accelerometer sensorembodiment of the present invention having passive means for locking theproof mass in a null position during periods of up or down or lateralaccelerations above predetermined threshold.

FIG. 9 illustrates the schematic of another accelerometer sensorembodiment of the present invention having passive means for locking theproof mass in a null position during periods of up or down or lateralaccelerations above predetermined threshold.

FIG. 10 illustrates the schematic of another accelerometer sensorembodiment of the present invention having passive means for locking theproof mass in a null position during periods of up or down accelerationsabove predetermined threshold. The proof mass of the accelerometer isnormally locked.

FIGS. 11 a and 11 b illustrate the schematic of one embodiment of themechanism for locking the keeping the proof mass locked to the basestructure of the sensor in normal conditions.

FIG. 12 illustrates the schematic of another accelerometer sensorembodiment of the present invention having toggle mechanism type ofpassive means for locking the proof mass in a null position duringperiods of up or down accelerations above predetermined threshold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although this invention is applicable to numerous and various types ofsensors and external stimulus, it has been found particularly useful inthe environment of accelerometers and inertia based gyros andacceleration stimulus. Therefore, without limiting the applicability ofthe invention to accelerometers and gyros and acceleration stimulus, theinvention will be described in such environment.

In summary, the inertia based sensors provide a general method ofpassively hardening various sensors with moving parts and/or withsignificant structural flexibility (compared to their base structure),particularly for application in devices that are susceptible to shockloading from different directions, residual vibration as the result ofshock or similar high acceleration loading such as accidental drops. Inparticular, for munitions applications, such as for gun-fired munitionsand mortars, there is provided sensors such as accelerometers andinertia based gyros that that are not only hardened against shockloading due to accidental drops and firing setback and set-forwardaccelerations, but by allowing the proof mass (inertia) and movingelements of the sensors to be locked to the sensor base structure whensuch acceleration levels are beyond certain predetermined threshold, thesize of the proof mass (inertia) elements can be significantlyincreased, thereby also significantly increasing sensitivity of suchinertia based sensors. The method by which this is achieved isapplicable to all such sensors, but is of particular importance fordevices, such as sensors, such as accelerometers and inertia basedgyros, actuators and the like that are desired to be light weighttherefore structurally flexible or are required to be light weight orhighly deformable (flexible) or have movable parts for their properoperation or to render them highly sensitive to the input to be measuredsuch as for the case of almost all accelerometers and/or inertia basedgyros, such as inertia measurement units (IMUs).

In the context of the present invention, hardening is meant to refer tothe following functions: (1) Provision of means to protect the movingparts and various mechanisms of the sensor from physical short term orpermanent damage and/or (2) To minimize or effectively eliminateresidual vibration of the components of the sensor that would requiretime to settle before the device could begin or resume its normaloperation. The residual vibration is generally due to the elasticdeformation of one or more movable components of the sensor and resultin a certain amount of potential energy to be stored in these componentsduring shock loading and would cause residual vibration until it isabsorbed (damped) by passive or active means.

The disclosed embodiments for MEMS accelerometers and inertia basedgyros are general in design and are applicable to all basic designs thatinclude elastic and/or moving elements, e.g., all those based ontorsional deformation, bending deformation, axial deformation and theirvarious combinations.

The basic operation of the various embodiments of the sensors is basedon locking one or more moving components of the sensor to a relativelyrigid base structure of the sensor (accelerometer or inertia based gyro)during the period(s) in which the sensor experiences shock loading thatis beyond certain predetermined threshold. In an accelerometer, thismoving component is referred to as a proof mass (and/or other movingcomponents of the accelerometer to which the proof mass is rigidlyattached). In the embodiments, the locking or braking action of themoving component and the mechanism of its operation may be described asbeing passive, i.e., require no external power and its operation isautomatically triggered when the acceleration levels reach certainpreset levels. A difference between the embodiments disclosed and thosedisclosed in previous art (the U.S. Pat. No. 6,626,040) is that theembodiments disclosed in the prior art can protect the proof mass andmoving parts of the sensor from high acceleration levels (shock loading)applied from only one direction (such as only from the firing setbackacceleration and not from the firing set-forward acceleration for thecase of gun-fired munitions, mortars and the like), thereby making themundesirable for applications such as for munitions applications. Incontrast, however, the embodiments can protect the proof mass and othermoving components of the sensor from multi-directional shock, such asfrom the firing setback acceleration as well as from the firingset-forward acceleration for the case of gun-fired munitions, mortarsand the like, thereby making them highly suitable for such munitionsapplications.

In addition, the locking mechanism may have the means to lock the proofmass or the aforementioned moving component(s) to which it is rigidlyattached, at a predetermined position corresponding to an accelerationoffset, usually at a level close to the level at which the accelerationmeasurements have to be resumed following unlocking of the proof mass orthe aforementioned moving component(s). The offset may be programmableinto the sensor, in which case external power would generally berequired to activate some actuation means to affect and/or vary theoffset level. The offset may also be actively set or built into thesensor, in which case external power is not required to put it intoeffect.

In the following description, the aforementioned sensors and methods ofhardening the sensors and the various embodiments of their applicationare described in terms of accelerometers in general, and those designedto be produced using MEMS (microelectromechanical devices) technology inparticular. However, it can be appreciated by those of ordinary skill inthe art that the disclosed sensors and methods are readily applicable toall devices, such as various sensors and actuators with moving parts,particularly those constructed with flexible and/or moving elements fortheir proper operation or for reasons such as to reduce weight (mass orinertia). The sensors and methods are at least partly used to providethe means to lock or brake the primary moving components of varioussensors that are subject to shock loading to protect them from damageduring shock loading and where appropriate, to minimize residualvibration and settling time.

A first embodiment 200 is shown in the schematic drawing of FIG. 2 a.The accelerometer 200 shown schematically therein, is intended tomeasure acceleration in directions 220 and 221. The accelerometer 200consists of a proof mass 212 which is rigidly attached to a relativelyrigid base 213 (plate), a cantilever (bending) type of elastic element211 with an equivalent spring rate k at the location of the proof mass212 and in the direction of the acceleration 220 (221). The proof mass212 (with mass m) is located a distance 215 (with length l) from thebase 205 to which the elastic beam element 211 is rigidly attached. Inmost MEMS types of accelerometers, the displacing plate 213 forms oneside of a capacitor while the other capacitor plate (not shown) isrigidly attached to the base 205. This capacitor will then form thesensor that measures the elastic displacement of the proof mass due tothe acceleration in the directions 220 and 221.

The basic mechanism for the aforementioned locking of the proof mass 212consists of a mass 207 which is attached close to the mid-point of aflexible beam 201, preferably by a hinge joint 218. The flexible beam201 is fixed to the base structure of the sensor 205, such as by a hingejoint 202 on one side and to a relatively rigid link 204 by a hingejoint 203. The relatively rigid link 204 is in turn attached to the basestructure of the sensor 205 by a hinge joint 206. The hinge joints 202,203 and 206 can be conventional hinges or living joints. The means oflocking the proof mass 212 during high acceleration events(accelerations being in the direction indicated by the arrow 220 or thearrow 221) comprises a member 219, which is fixed to an end 208 of thelink 204. The member 219 can have a u-shaped mouth 210 with a taperedleading edge 209 to capture an edge 214 or other portion of the plate211 when it is to be essentially locked to the base structure 205 of thesensor 200.

If the sensor 200 is subjected to a high acceleration level in thedirection of the arrow 220 (221), the dynamic force resulting from theaction of the acceleration on the inertia (mass) of the element 207 willdeflect the beam 201 downward (upward) as shown by solid lines in FIG. 2b (shown by dotted lines in FIG. 2 b), thereby causing the link 204 torotate in the counter-clockwise direction, thereby moving the lockingmember 219 into position to engage the edge 214 of the plate 211 andessentially locking the plate 211 to the base structure of the sensor205 as shown in FIG. 2 b.

In general, the flexible beam 201 is preferably provided with stops 216and 217 to protect the beam 201 from bending beyond the required levels.The bending stiffness of the flexible beam 201 is also preferablyselected such that at the aforementioned predetermined accelerationthresholds, the upward or downward bending of the flexible beam wouldposition the locking member 219 in the position to engage the edge 214of the plate 211. In addition, preloaded spring elements (not shown) mayalso be provided between the flexible beam 201 and the base structure ofthe sensor 205 that have to be overcome before the flexible beam 201would begin to deflect.

The locking mechanism of the embodiment of FIGS. 2 a and 2 b is therebyshown to be capable of operating to lock the proof mass or other movingcomponents of a sensor when the sensor is subjected to accelerationlevels above certain thresholds, irrespective of its sense (in the caseof the sensor of FIGS. 2 a and 2 b, if the acceleration is in either 220or 221 direction).

In an alternative embodiment 250 shown in FIG. 3 a, the flexible beam201 of the embodiment 200 shown in FIG. 2 a is replaced with tworelatively rigid links 251 and 252. In the schematic of FIG. 3 a, allother members of the embodiment 250 are identical to those of theembodiment 200 of FIG. 2 a. The link 251 is similarly attached on oneend to the base structure of the sensor 205 by the hinge joint 202 andon the other end by the hinge joint 253 to the link 252. The other endof the link 252 is attached to the link 204 by the hinge joint 203. Themass element 217 in then preferably attached directly to the hinge joint253 (instead of the hinge joint 218 in the embodiment 200 of FIG. 2 a).The relatively rigid links 251 and 252 are provided with preloadedtorsion springs at the joint 253 (preferably a pair of opposingpreloaded torsion springs—not shown) to bias the beams 251 and 252 tostay at or near their collinear configuration as shown in FIG. 3 a. Inkinematics theory, this collinear configuration of the two links 251 and252 is known as their singular position, the use of which has been shownto be the only way of obtaining a single positioning (single directionof displacement or rotation of a link (in the case of the embodiment ofFIG. 3 a, the counter-clockwise rotation of the link 204) for twoopposite displacements or rotations of an input link (in the case of theembodiment of FIG. 3 a, the clockwise and counter-clockwise rotation ofthe link 251—in this case caused by the accelerations in the directions221 and 220, respectively, acting on the mass element 207).

Now if the sensor is subjected to a high acceleration level in thedirection of the arrow 220 (221), the dynamic force resulting from theaction of the said acceleration on the inertia (mass) of the element 207will cause the element 207 (thereby the joint 253 of the links 251 and252) to be displaced downward (upward) as shown by solid lines in FIG. 3b (shown by dotted lines in FIG. 3 b), thereby causing the link 204 torotate in the counter-clockwise direction, thereby moving the lockingmember 219 into position to engage the edge 214 of the plate 211 andessentially locking the plate 211 to the base structure of the sensor205 as shown in FIG. 3 b.

In general, the assembly of links 251 and 252 can be provided with stops216 and 217 to protect the assembly from displacing beyond the requiredlevels. The net torsional spring rate and the preloading level of theaforementioned torsion springs at the joint 253 can also be selectedsuch that at the aforementioned predetermined acceleration thresholds,the upward or downward displacement of the joint 253 would position thelocking member 219 in the position to engage the edge 214 of the plate211. In addition, preloaded torsion spring elements (not shown) may alsobe provided with different preload levels (generally providing acorresponding initial upward or downward displacement of the joint 253)so that the acceleration threshold level that results in the engagementof the locking member 219 with the edge 214 of the plate 211 isselectively different for acceleration in the upward direction (i.e.,the direction of the arrow 220) and acceleration in the downwarddirection (i.e., the direction of the arrow 221).

A basic mechanism to lock the proof mass 212 and/or other movingcomponents of an accelerometer is described above for the embodiments ofFIGS. 2 a and 3 a. The design, however, can be seen to be applicable toalmost all accelerometer and inertia based gyro designs, particularlythose constructed using MEMS technology.

Those skilled in the art will appreciate that a number of variations ofthe designs that are illustrated in FIGS. 2 a and 3 a may also beutilized for the construction of the locking mechanism. The onlyrequirement of such locking mechanisms is that for both up or downmotion of the locking action initiating mass element (in the case of theembodiment of FIG. 2 a, the mass 207), the locking member (in the caseof the embodiment of FIG. 2 a, the member 219) move in the samedirection, i.e., the direction to engage the proof mass or other movingcomponents of the sensor.

Another embodiment 300 is shown in the schematic of FIG. 4 a. In theschematic of FIG. 4 a, except for the locking mechanism portiondescribed below, all other members of the embodiment 300 are identicalto those of the embodiment 200 of FIG. 2 a. In this embodiment 300, thelocking mechanism consists of the locking member 301, which ispositioned in a guide in which it can slide laterally as shown in FIG. 4a (in this schematic, the sliding members are shown as two sets ofrollers 302 and 303 positioned on either side of the locking member301), thereby forming a so-called sliding joint. The member 301 can beprovided with a u-shaped mouth 304 having a tapered leading edge 305 tocapture the edge 214 of the plate 211 when it is to be essentiallylocked to the base structure 205 of the sensor 300. The locking member301 is provided with inclined surfaces 306 and 307. The lockingmechanism is also provided with the relatively rigid links 310 and 311,which are attached to the base structure 205 of the sensor 300 by thehinge joints 312 and 313, respectively. The links 310 and 311 areprovided with springs 314 and 315, which are both attached to the basestructure of the sensor 205 on one end, and to the links 310 and 311,respectively, at the other end. The springs 314 and 315 are preloaded incompression, so that in normal conditions the links 310 and 311 arepressed against the stop 316. The stop 316 is attached to the basestructure of the sensor 205. In the normal conditions shown by theconfiguration of FIG. 4 a of the sensor 300, the locking member 301 ispushed back against the tips 308 and 309 of the links 310 and 311 by thespring element 318. It is noted that in the schematic of FIG. 4 a, forclarity, a compressively preloaded spring 318 is shown to be used.However, a tensile spring can also be used instead which can becentrally positioned relative to the locking member 301. The links 310and 311 can be provided with stops 319 and 320 to limit their rotationsuch that their tips 308 and 309 stays within the range of contact withthe surfaces 306 and 307, respectively.

Now if the sensor is subjected to a high acceleration level in thedirection of the arrow 321, the dynamic force resulting from the actionof the acceleration on the inertia of the link 311 (drawn with dottedlines in FIG. 4 b) will generate a torque that if it is large enough toovercome the forces of the springs 315 and 318, would begin to rotatethe link 311 in the clockwise direction. As a result, as the link 311 isrotated in the clockwise direction towards its uppermost positionindicated by solid lines in FIG. 4 b (enumerated in this position withthe numeral 323), the tip 309 of the link 311 would push the lockingmember 301 into position to engage the edge 214 of the plate 211 andessentially locking the plate 211 to the base structure of the sensor205 as shown in FIG. 4 b. On the other hand, if the sensor is subjectedto a high acceleration level in the direction of the arrow 322, thedynamic force resulting from the action of the said acceleration on theinertia of the link 310 (drawn with dotted lines in FIG. 4 b) willgenerate a torque that if it is large enough to overcome the forces ofthe springs 314 and 318, would begin to rotate the link 310 in thecounterclockwise direction. As a result, as the link 310 is rotated inthe counterclockwise direction towards its lowermost position indicatedby solid lines in FIG. 4 b (enumerated in this position with the numeral324), the tip 308 of the link 310 would push the locking member 301 intoposition to engage the edge 214 of the plate 211 and essentially lockingthe plate 211 to the base structure of the sensor 205 as shown in FIG. 4b.

Another embodiment 350 is shown in the schematic of FIG. 5 a. In theschematic of FIG. 5 a, except for the locking mechanism portiondescribed below, all other members of the embodiment 350 are identicalto those of the embodiment 200 of FIG. 2 a. In this embodiment 350, thelocking mechanism consists of the locking member 351, which ispositioned in a guide in which it can slide laterally as shown in FIG. 5a (in this schematic, the sliding members are shown as two sets ofrollers 352 and 353 positioned on either side of the locking member351), thereby forming a so-called sliding joint. The member 351 isprovided with a u-shaped mouth 354 having a tapered leading edge 355 tocapture the edge 214 of the plate 211 when it is to be essentiallylocked to the base structure 205 of the sensor 350. The locking member351 is provided with inclined surfaces 356 and 357. The locking member351 is provided with a v-shaped portion indicated by its two surfaces356 and 357 opposite to the u-shaped mouth 354. The locking mechanism isalso provided with a relatively rigid member 358, which is free to slideup and down as shown in FIG. 5 a over the surface 359 of the basestructure of the sensor, if possible over rolling or other similarfriction reduction elements 360. The member 358 is held in place by thespring element 361, which is attached to the member 358 on one side andto the base structure of the sensor on the other side, preferably byhinge joints (not shown). The spring element 361 is preferably preloadedin tension in the normal configuration of the sensor shown in FIG. 5 a.The member 358 is provided with inclined surfaces 362 and 363 thatmatches the sides of the v-shaped surfaces 356 and 357, respectively, ofthe locking member 351 as shown in the schematic of FIG. 5 a. Inaddition, stops 370 and 371 are preferably provided to limit up and downtranslation of the element 358 to prevent it from being disengaged fromthe locking member 351.

In the normal condition shown by the configuration of FIG. 5 a of thesensor 350, the locking member 351 is pushed back against the member 358by the spring element 364, bringing the surfaces 356 and 357 of thev-shaped portion of the locking member 351 in contact with the surfaces362 and 362, respectively, of the element 358. The spring element 364 isattached to the base structure of the sensor 205 on one end and to thelocking member 351 on the other. The spring element 364 can also bepreloaded in compression. It is noted that in the schematic of FIG. 5 a,for clarity, a compressively preloaded spring 364 is shown to be used.However, a tensile spring can also be used instead and can be centrallypositioned relative to the locking member 351.

If the sensor is subjected to a high acceleration level in the directionof the arrow 365, the dynamic force resulting from the action of theacceleration on the inertia of the element 358 will generate a forcethat if it is large enough to overcome the forces exerted by the springelement 361 and the vertical component of the contact force across thesurface of contact (between the surfaces 356 and 362) generated by thespring element 364 (neglecting friction and other present resistiveforces), it would begin to force the element 358 to translate uprelative to the locking member 351. As a result, as the member 358translates up towards its uppermost position indicated in FIG. 5 b bythe numeral 367, thereby the locking member 351 is pushed into positionto engage the edge 214 of the plate 211 and essentially locking theplate 211 to the base structure of the sensor 205 as shown in FIG. 5 b.On the other hand, if the sensor is subjected to a high accelerationlevel in the direction of the arrow 366, the dynamic force resultingfrom the action of the acceleration on the inertia of the element 358will generate a force that if it is large enough to overcome the forcesexerted by the spring element 361 and the vertical component of thecontact force across the surface of contact (between the surfaces 357and 363) generated by the spring element 364 (neglecting friction andother present resistive forces), it would begin to force the element 358to translate down relative to the locking member 351. As a result, asthe member 358 translates down towards its lowermost position (oppositeto the position 367 of the element 351 shown in FIG. 5 b), therebysimilarly causing the locking member 351 to be pushed into position toengage the edge 214 of the plate 211 and essentially locking the plate211 to the base structure of the sensor 205 as shown in FIG. 5 b for theacceleration in the direction of the arrow 365.

In the schematic of FIG. 6 a, the sensor portion of the embodiment 400is the same as that of the embodiment 200 shown in the schematic drawingof FIG. 2 a, except that a relatively rigid and u-shaped element 401 isrigidly attached to the end 402 of the cantilever type of elasticelement 211 as shown in FIG. 6 a. In the schematic of FIG. 6 a, thelocking mechanism consists of two similar mechanisms 403 and 404,constructed with relatively rigid links 405 and 406, which are attachedto the base structure of the sensor 205 by the hinge joints 407 and 408,respectively. The links 405 and 306 are provided with mass elements 409and 410 on one end and the locking members 411 and 412 on the other end,respectively. The locking members 411 and 412 are each provided withu-shaped mouths 413 and 414 with tapered leading edges 415 and 416,respectively. The u-shaped mouths 413 and 414 are positioned such thatwith proper rotation of the links 405 and 306, they could capture theedges 417 and 418 of the u-shaped element 401, respectively, when theplate 211 it is to be essentially locked to the base structure 205 ofthe sensor 400. The links 405 and 406 are each provided with a springelement 419 and 420, which are attached to the base structure of thesensor 205 on one end and to the links 405 and 406, respectively, on theother end. The spring elements 419 and 420 are preferably preloaded intension such that in the normal condition of the sensor 400, the links405 and 406 are held against the stops 421 and 422, respectively.

Now if the sensor is subjected to a high acceleration level in thedirection of the arrow 423, the dynamic force resulting from the actionof the acceleration on the inertia of the mass element 409 of thelocking mechanism component 403 will generate a torque that if it islarge enough to overcome the force of the spring element 419, wouldbegin to rotate the link 405 in the clockwise direction. As a result, asthe link 405 is rotated in the clockwise direction, the locking member411 is moved into position to engage the edge 417 of the u-shaped member401, which is fixedly attached to the plate 211 and essentially lockingthe plate 211 to the base structure of the sensor 205 as shown in FIG. 6b. In the meantime, the acceleration in the direction of the arrow 423acts on the mass element 410 of the locking mechanism component 404 andsimilarly generates a torque that would tend to rotate the link 406 inthe counter-clockwise direction, thereby pressing the link 406 againstthe stop 422. Here, it is noted that it is assumed that the masselements 409 and 410 represent the net imbalanced mass of the rotatingelements of the locking mechanism components 403 and 404 acting certaindistance to the right of the hinge joints 407 and 408, respectively.

On the other hand, if the sensor is subjected to a high accelerationlevel in the direction of the arrow 424, the dynamic force resultingfrom the action of the acceleration on the inertia of the mass element410 of the locking mechanism component 404 and will generate acounter-clockwise torque that if it is large enough to overcome theforce of the spring element 420, would begin to rotate the link 406 inthe counter-clockwise direction. As a result, as the link 406 is rotatedin the counter-clockwise direction, the locking member 412 is moved intoposition to engage the edge 418 of the u-shaped member 401, which isfixedly attached to the plate 211 and essentially locking the plate 211to the base structure of the sensor 205 (not shown in FIG. 6 b). In themeantime, the acceleration in the direction of the arrow 424 acts on themass element 409 of the locking mechanism component 403 and similarlygenerates a torque that would tend to rotate the link 405 in thecounter-clockwise direction, thereby pressing the link 405 against thestop 421 as shown in its configuration of FIG. 6 a. Here, it is notedthat it is assumed that the mass elements 409 and 410 represent the netimbalanced mass of the rotating elements of the locking mechanismcomponents 403 and 404 acting certain distance to the right of the hingejoints 407 and 408, respectively.

Those skilled in the art will appreciate that a number of variations ofthe embodiments of FIGS. 2-6 may be constructed to perform the sametasks, i.e., to essentially lock the proof mass (inertia element) if thesensor is accelerated beyond a predetermined level (threshold) in twoopposite directions, e.g., for the particular use of gun-fired munitionsand mortars, during the firing setback as well as set-forwardaccelerations.

It is also appreciated by those skilled in the art that various featuresof the embodiments of FIGS. 2-6 may be combined to arrive at alternativedesigns that can perform the same aforementioned tasks. An example of anembodiment with such combined features is shown in FIG. 7 a andindicated as embodiment 450. The accelerometer embodiment 450 shown isintended to measure acceleration in the directions 451 and 452. In theschematic of FIG. 7 a, except for the locking mechanism portiondescribed below, all other members of the embodiment 450 are identicalto those of the embodiment 200 of FIG. 2 a. In addition, identicallocking member 219, attached to the relatively rigid link 204, which isin turn attached to the base structure of the sensor 205 by a hingejoint 206 as shown in the embodiment 200 of FIG. 2 a are used in thepresent embodiment 450 of FIG. 7 a. To the end 453 of the link 204,however, is fixedly attached the member 454, which has a v-shapedfeature on its surface as shown in FIG. 7 a, with inclined surfaces ofthe v-shaped feature indicated by numerals 455 and 456. A compressivelypreload spring element 457 is also provided that is attached to the basestructure of the sensor 205 on one end and to the link 204 on the other.In normal conditions, the compressively preloaded spring element 457forces the link 204 to rest against the stop 458, which is also attachedto the base structure of the sensor 205. The locking mechanism is alsoprovided with a relatively rigid link 459, which is attached to the basestructure of the sensor 205 by a hinge joint 460. The link 459 is alsoprovided with opposing spring elements 461 and 462, which are attachedto the base structure of the sensor on one end and to the link 459 onthe other end. The spring elements 461 and 462 are preloaded with equalamount of force such that in normal conditions, the link 459 is at restin its middle position relative to the member 454 as shown in FIG. 7 a.The link 459 is provided with the relatively round tip 463, which in thenormal conditions positioned centrally with the v-shaped feature of theelement 454.

The preloading forces in the spring elements 461 and 462 can be tensile,even though compressive forces may also be used. The spring rates of thespring elements 461 and 462 may, however, be selected to be different toallow the locking mechanism to lock the proof mass 212 at differentacceleration threshold in the directions of the arrows 451 and 452.Alternatively, the spring elements may be torsional or of any othertype. The hinge joint 460 can also be a living joint, and is preferablyconstructed with enough spring rate in torsion (i.e., provide enoughelastic resistance in torsion) to serve the functionality of the springelements 461 and 462 (in which case no preloading forces/torques ormoments will in general be required). The link 459 is provided withstops 464 and 465 to limit the link clockwise and counter-clockwiserotation, respectively, so that the tip 463 would always stay within therange of the surfaces of contact 455 and 456 of the v-shaped feature ofthe element 454.

If the sensor is subjected to a high acceleration level in the directionof the arrow 451, the dynamic force resulting from the action of theacceleration on the inertia of the link 459 will generate a torque thatwould tend to rotate the link 459 in the clockwise direction. If theacceleration level is high enough to overcome the resistance of thespring elements 461 and 462, then the link 459 is rotated clockwise upto the stop 464. As the link 459 is rotated in the clockwise direction,the tip 463 of the link 459 pushes against the surface 456 of theelement 454, thereby causing the link 204 to rotate in thecounter-clockwise direction, thereby moving the locking member 219 intoposition to engage the edge 214 of the plate 211 and essentially lockingthe plate 211 to the base structure of the sensor 205, as shown in FIG.7 b. If the sensor is subjected to a high acceleration level in thedirection of the arrow 452, the dynamic force resulting from the actionof the acceleration on the inertia of the link 459 will generate atorque that would tend to rotate the link 459 in the counter-clockwisedirection. If the acceleration level is high enough to overcome theresistance of the spring elements 461 and 462, then the link 459 isrotated counter-clockwise up to the stop 465. As the link 459 is rotatedin the counter-clockwise direction, the tip 463 of the link 459 pushesagainst the surface 455 of the element 454, thereby causing the link 204to rotate in the counter-clockwise direction, thereby moving the lockingmember 219 into position to engage the edge 214 of the plate 211 andessentially locking the plate 211 to the base structure of the sensor205 (not shown). As a result, the locking mechanism of this embodimentwould lock the proof mass if the sensor is subjected to aforementionedhigh acceleration levels in either upward (451) or downward (452)direction, which for gun-fired munitions and mortars can correspond tofiring setback and set-forward accelerations.

The locking mechanisms of the embodiments of FIGS. 2-7 were shown toprovide for essentially locking the proof mass (inertia element) ofinertia based sensors to the base structure of the sensor when thesensor is accelerated in either direction along (and close to) a certainline. For the particular case of gun-fired munitions and mortars and thelike, the line of acceleration action is considered to be essentiallyparallel to the direction of firing setback and set-forwardaccelerations. In general, an inertia based sensor such as anaccelerometer or gyro is required to be protected from high levels ofaccelerations that are essentially parallel (or have a substantialcomponent) to the directions along which the inertia element of thesensor is intended to be subjected to the sensory acceleration signal totranslate and/or rotate the inertia or generate a dynamic force and/ortoque and/or moment. Such sensors are, in general, relativelyunresponsive to sensor accelerations in directions that aresubstantially perpendicular to the required sensory response direction,and do not generally require protection for their proof mass (inertiaelements) against shock induced accelerations in the latter directions.This is even true for gun-fired munitions, mortars and the like sincethe high firing accelerations are always applied axially to theprojectile (in the direction of firing) and not in the lateraldirection. However, if the projectile is accidentally dropped, thedirection of impact induced acceleration is unpredictable and may bedirected laterally. But since most inertia based sensors (accelerometersand gyros), particularly those that have high sensitivity, are designedwith structures similar to those shown in FIGS. 1-7, i.e., withrelatively low resistance to proof mass (inertia element) motion in onedirection and significant resistance in other directions, therefore ifthe proof mass (inertia element) and other moving elements of the sensorare protected against high acceleration levels in the direction of theintended sensory measurements (as they are in the embodiments of FIGS.2-7), then the sensor can be expected not to require similar proof mass(inertia element) protection against similarly high acceleration levelsexperienced from other directions.

On the other hand, if in certain applications, such as in certainmulti-axis inertia based sensor, the sensor is designed with proofmasses (inertia elements) that respond to accelerations from many(independent) directions (e.g., the aforementioned axial and lateraldirections), then the locking mechanisms of the embodiments of FIGS. 2-7may be modified to lock the proof mass (inertia element) when the sensoris subjected to both axial and/or lateral directions. The requiredmodifications generally involve the addition/repositioning of the mass(inertia) element that “actuates” the sensor proof mass (inertiaelement) locking mechanism, and/or by providing additional “actuation”mechanisms that respond to high laterally applied acceleration levels.Such implementation of the aforementioned modifications is illustratedby the following two example embodiments.

The schematic of the first modified embodiment 430 is shown in FIG. 8.The embodiment 430 is obtained by the following modification of theembodiment 400 illustrated in the schematic of FIG. 6 a. In theembodiment 430, except for the following indicated modifications, allits elements are identical to those of the embodiment 400 and areidentically enumerated. Firstly, the mass elements 409 and 410 of theembodiment 400 (enumerated as mass elements 431 and 432, respectively,in FIG. 8) are positioned on or close enough to the horizontal lines (inthe plane of FIG. 8) passing through the hinge joints 407 and 408,respectively, so that when the sensor is subjected to accelerations inthe directions of the arrows 437 or 438, the dynamic force acting on theinertia of the mass elements 431 and 432 does not generate a substantialtorque about axes normal to the plane of FIG. 8, that would otherwisetend to rotate the locking elements 403 and 404. Secondly, a masselement 433 is attached to the link 405 between the hinge joint 407 andthe element 411 as shown in FIG. 8. Thirdly, a mass element 434 isattached to the extended end 439 of the link 406 as shown in FIG. 8.

If the sensor is subjected to a high acceleration level in the directionof the arrow 437, the dynamic force resulting from the action of theacceleration on the inertia of the mass element 433 of the lockingmechanism component 403 will generate a clockwise torque that if it islarge enough to overcome the force of the spring element 419, wouldbegin to rotate the link 405 in the clockwise direction. As a result, asthe link 405 is rotated in the clockwise direction, the locking member411 is moved into position to engage the edge 417 of the u-shaped member401, which is fixedly attached to the plate 211 and essentially lockingthe plate 211 to the base structure of the sensor 205, similar to thatshown in the schematic of FIG. 6 b. On the other hand, the accelerationin the direction of the arrow 437 acts on the inertia of the masselement 434 to generate a clockwise torque that would tend to rotate thelink 406 in the clockwise direction, pressing the link 406 against thestop 422, as shown in FIG. 8.

However, if the sensor is subjected to a high acceleration level in thedirection of the arrow 438, the dynamic force resulting from the actionof the acceleration on the inertia of the mass element 434 of thelocking mechanism component 404 will generate a counter-clockwise torquethat if it is large enough to overcome the force of the spring element420, would begin to rotate the link 406 in the counter-clockwisedirection. As a result, as the link 406 is rotated in thecounter-clockwise direction and the locking member 412 is moved intoposition to engage the edge 418 of the u-shaped member 401—which isfixedly attached to the plate 211—and essentially locking the plate 211to the base structure of the sensor 205 (not shown in FIG. 8). In themeantime, the acceleration in the direction of the arrow 437 acts on themass element 433 of the locking mechanism component 403 and similarlygenerates a counter-clockwise torque that would tend to rotate the link405 in the counter-clockwise direction, thereby pressing the link 405against the stop 421 as shown in its configuration of FIG. 8.

The schematic of the second modified embodiment 480 is shown in FIG. 9.The embodiment 480 is obtained by the following modification of theembodiment 350 illustrated in the schematic of FIG. 5 a. In theembodiment 480, except for the following indicated modifications, allits elements are identical to those of the embodiment 350 and areidentically enumerated. Firstly, extensions 481 and 482 are provided tothe locking member 351. Secondly, links 483 and 484, which are attachedto the base structure of the sensor 205 by the hinge joints 485 and 486,respectively, are provided as shown in FIG. 9. Mass elements 487 and 488are attached to the links 483 and 484, respectively, as shown in FIG. 9.Spring elements 489 and 490, preloaded in compression, are provided andpositioned as shown in FIG. 9 to hold the links 483 and 484 against thestops 491 and 492, respectively, when the sensor 480 is in its normalcondition. It is noted that in the schematic of FIG. 9 and for the sakeof clarity, the spring elements 489 and 490 are shown to be positionedsuch that they can force the links 483 and 484 against the stops 491 and492. However, in practice, the spring elements 489 and 490 are can bepositioned on the opposite sides of the links 483 and 484 to performtheir tasks while preloaded in tension instead. In addition, the hingejoints 485 and 486 can be living joints and can be integrated springelements 489 and 490.

If the sensor is subjected to a high acceleration level in the directionof the arrow 493, the dynamic force resulting from the action of thesaid acceleration on the inertia of the element 487 will generate atorque in the clockwise direction that if it is large enough to overcomethe force exerted by the spring elements 489 and 364, would rotate thelink 483 in the clockwise direction. As a result, as the link 483 turnsin the clockwise direction, and its tip 495 would push against thesurface of the extension 381, thereby pushing the locking member 351into position to engage the edge 214 of the plate 211 and essentiallylocking the plate 211 to the base structure of the sensor 205 as shownin FIG. 5 b. In the meantime, the acceleration acts on the inertia ofthe mass element 488, generating a torque in the clockwise directionthat would force the link 484 against the stop 492.

However, if the sensor is subjected to a high acceleration level in thedirection of the arrow 494, the dynamic force resulting from the actionof the said acceleration on the inertia of the element 488 will generatea torque in the counter-clockwise direction that if it is large enoughto overcome the force exerted by the spring elements 490 and 364, wouldrotate the link 484 in the counter-clockwise direction. As a result, asthe link 484 turns in the counter-clockwise direction, and its tip 496would push against the surface of the extension 382, thereby pushing thelocking member 351 into position to engage the edge 214 of the plate 211and essentially locking the plate 211 to the base structure of thesensor 205 as shown in FIG. 5 b.

It is noted that in the embodiments of FIGS. 2-9, the proof mass(inertia) and other moving parts of the sensor is normally unlocked. Incertain applications, however, it is desirable to keep the proof mass(inertia element) and generally other moving parts of the sensor lockedto the base structure of the sensor until certain event is detected. Forexample, it might be desirable to keep the proof mass (inertia element)and other moving parts of a sensor that is designed to be highlysensitive to be protected from environmental noise such as vibrationduring transportation and other even minor shock loadings such as thoseexperienced during the manufacturing and assembly processes. For theparticular case of gun-fired munitions, mortars and the like, the eventthat would unlock the proof mass (inertial element) and other movingparts of the sensor will then preferably be the firing setback orset-forward acceleration, in particular, preferably the firingset-forward acceleration. Such inertia based sensors with normallylocked proof mass (inertia element) and other moving parts may beobtained by modifying the locking mechanisms of the embodiments of FIGS.2-9. The required modification generally involves the addition ofappropriate inertia actuated elements that would normally lock the proofmass (inertia element) locking member in its locking position. Then whenthe sensor experiences the intended acceleration (linear or rotary)event, for example, once the sensor experiences the firing setback (orset-forward) acceleration, then the added locking member disengages fromthe proof mass locking member, thereby rendering the sensor operational.To illustrate the aforementioned modification, the embodiment of FIG. 5a is modified as described below to obtain a sensor in which the proofmass (inertia element) and other moving parts of the sensor would beessentially locked to the base structure of the sensor in normalconditions. The resulting sensor is then shown to be capable of beingreadily adapted for use in three different operational scenarios. In thefirst operational scenario, the proof mass (inertia element) and othermoving parts of the sensor are essentially locked to the base structureof the sensor in normal conditions, and released as a result of arelatively high acceleration level in one direction (e.g., in thedirection of firing setback acceleration for the case of sensors used ingun-fired munitions, mortars and the like). In the second operationalscenario, the proof mass (inertia element) and other moving parts of thesensor are essentially locked to the base structure of the sensor innormal conditions, stay essentially locked during a relatively highacceleration level in one direction, and released as a result of arelatively high acceleration level in the second (e.g., opposite)direction (e.g., stay locked as a result of firing setback accelerationand release as a result of set-forward acceleration for the case ofsensors used in gun-fired munitions, mortars and the like). In the thirdoperational scenario, the proof mass (inertia element) and other movingparts of the sensor are unlocked from the base structure of the sensorin normal conditions, but become essentially locked to the basestructure of the sensor as a result of a relatively high accelerationlevel in one direction, and released as a result of a relativelyacceleration level in the second (e.g., opposite) direction (e.g.,become locked as a result of firing setback acceleration and release asa result of set-forward acceleration for the case of sensors used ingun-fired munitions, mortars and the like). Such an embodiment ispresented below.

The basic design of an inertia based sensor for operation in theaforementioned three scenarios is described by the example of theembodiment 500 illustrated in the schematic drawing of FIG. 10. Theembodiment 500 is obtained by the following modification of theembodiment 350 illustrated in the schematic of FIG. 5 a. In theembodiment 500, except for the following indicated modifications, allits elements are identical to those of the embodiment 350 and areidentically enumerated. Firstly, locking member 501 (indicated bynumeral 351 in FIG. 5 a) is provided with a recess 502. In theconfiguration shown in FIG. 10, the locking member 501 is in position toengage the edge 214 of the plate 211 and essentially locking the plate211 to the base structure of the sensor 205 as described for theembodiment 350 of FIG. 5 b. The locking member 501 is held in thisposition against the force of the spring element 364 by the lockingelement 503, which can slide up and down in the guide 504, which isfixed to the base structure of the sensor 205. The locking element 503is kept engaged to the locking member 501 by the force exerted by thecompressively preloaded spring element 505 on the top surface of thelocking element 503. The sensor is also provided with a “latching”element 507, which can slide back and forth in the guide 508, which isfixed to the base structure of the sensor 205. The spring element 509 isprovided, which is attached to the base structure of the sensor 205 onone end and to the base of the latching element 507 on the other end asshown in FIG. 10. The element 507 is held the shown position, i.e., withthe tip 510 over the extended end 506 of the locking element 503,preferably with the sloped surface 511 in contact with the said tip 510as shown in FIG. 10.

In the normal configuration shown in FIG. 10, the spring elements 505and 509 are preferably preloaded in compression such that if the sensor500 is subjected to acceleration levels of up to a certain threshold inthe direction of the arrow 365, the dynamic force generated by theaction of the acceleration on the inertia of the locking element 503 isnot enough to overcome the forces exerted by the spring elements 505 and509. However, if the sensor 500 is subjected to high enough accelerationlevels in the direction of the arrow 365, then the dynamic forcegenerated by the action of said acceleration on the inertia of thelocking element 503 would overcome the forces exerted by the springelements 505 and 509, thereby allowing the locking element 503 totranslate up and disengage recess 502 of the locking member 501. Duringthis process, the locking element 503 would also force the latchingelement 507 away from its path of translation by applying a force to theinclined surface 511 of the latching element 507. However, once thebottom surface 512 of the extended end portion 506 of the lockingelement 503 has passed the tip 510 of the latching element 507, the tip510 of the latching element 507 is pushed under the bottom surface 512of the extended end portion 506 of the locking element 503. As a result,when the aforementioned high acceleration level has ceased, the lockingelement 503 can no longer slide back down to engage the recess 502 ofthe locking member 501. The sensor 500 is thereby free to operate as waspreviously described for the embodiment 350 of FIG. 5 a.

The inertia sensor embodiment 500 of FIG. 10 is readily shown to becapable of operating in the aforementioned first and second operationalscenarios and with a simple modification, in the aforementioned thirdoperational scenario as follows.

To be employed for operation in the aforementioned first operationalscenario, the sensor 500 is oriented such that the firing setbackacceleration is in the direction of the arrow 365, FIG. 10. As a result,the proof mass 212 and other moving parts of the sensor 500 in normalconditions are essentially locked to the base structure of the sensor.The proof mass 212 and other moving parts of the sensor 500 are,however, released as a result of the firing setback acceleration asdescribed above and the sensor 500 becomes operational and operates aswas previously described for the embodiment 350 of FIG. 5 a.

To be employed for operation in the aforementioned second operationalscenario, the sensor 500 is oriented such that the firing setbackacceleration is in the direction of the arrow 366, FIG. 10. As a result,the proof mass 212 and other moving parts of the sensor 500 in normalconditions are essentially locked to the base structure of the sensorand stay locked during the period of firing setback acceleration sincethe acceleration causes the locking element 503 to be pressed downagainst the locking member 501 and thereby stay engaged in the recess502. The proof mass 212 and other moving parts of the sensor 500 are,however, released as a result of the firing set-forward acceleration,which would be in the direction of the arrow 365, thereby rendering thesensor 500 operable to function as was previously described for theembodiment 350 of FIG. 5 a.

To be employed for operation in the aforementioned third operationalscenario, the sensor 500 is oriented such that the firing setbackacceleration is directed in the direction of the arrow 366, FIG. 10. Theproof mass 212 and other moving parts of the sensor 500 are not lockedto the base structure of the sensor 205 by the locking member 501. Thelocking element 503 assembly is modified as described later and shown inthe schematic of FIGS. 11 a and 11 b so that during the setbackacceleration period, the locking element can pass the latching elementtip 510 and engage the recess 502 of the locking member 501, noting thatas a result of the applied setback acceleration, the element 358 wouldhave pushed the locking member 501 to engage the edge 214 of the plate211 and essentially locking the plate 211 to the base structure of thesensor 205 as described for the embodiment 350 of FIG. 5 b, therebylining up the recess 502 under the locking element 503. Then during theset-forward acceleration period, the sensor 500 is accelerated in thedirection of the arrow 365, thereby forcing the locking element 503 totranslate away from the locking member 501 and releasing it to operatefreely as was described for the embodiment 350 of FIG. 5 a.

The schematic of the modified assembly of the locking element 503 andthe latching element 507 is shown in the schematics of FIGS. 11 a and 11b. In this modification, the extended top portion 506 of the lockingelement 503 is attached to the locking element body 503 by a slidingjoint to allow it to slide from its centered position shown in FIGS. 10and 11 b to its right hand most position indicated by the numeral 520shown in FIG. 11 a. In its latter position, the element 506 clears thetip 510 of the latching element 507. A relatively rigid member 521 isfixedly attached to the side of the extended top portion 506 as shown inFIG. 11 a. In the configuration shown in FIG. 11 a (which corresponds tothe configuration in which the locking element is disengaged from thelocking member 501, FIG. 10), the member 521 is held against the member522, which is fixed to the base structure of the sensor 205. The springelement 523 is also provided, which is attached to the locking elementbody on one end and to the member 521 on the other and which ispreloaded in tension is used to provide a force that would tend to bringthe element 506 back to its centrally positioned location shown in FIGS.10 and 11 b, thereby keeping the elements 521 and 522 in constantcontact. Then as a result of the aforementioned firing acceleration inthe direction of the arrow 366, FIG. 10, the assembly of the extendedtop portion 506 and the locking element 503 is pushed downward, allowingthe element 506 to pass the latching element 507, following which theelement 521 passes the element 522, thereby allowing the spring element523 to pull the element 506 to its central position as shown in FIG. 11b.

An alternative embodiment for inertia based sensors to be employed foroperation in the aforementioned third operational scenario may beobtained by the use of a toggle type of mechanism. Such a mechanism maybe constructed, for example, by the following modification of theembodiment 200 of FIG. 2 a, illustrated in the schematic of FIG. 12 andindicated by the numeral 550. The embodiment 550 is obtained by thefollowing modification of the embodiment 200 illustrated in theschematic of FIG. 2 a. In the embodiment 550, except for the followingindicated modifications, all its elements are identical to those of theembodiment 200 and are identically enumerated. In the embodiment 550,the link 204 of the embodiment 200 of FIG. 2 a is replaced by the link551, which is attached to the base structure of the sensor 205 by thehinge joint 552. The element 219 with the u-shaped mouth 210 and taperedleading edge 209 which is identical to that of embodiment 200 of FIG. 2a is attached to the end 553 of the link 551 to similarly capture theedge 214 of the plate 211 when it is to be essentially locked to thebase structure 205 of the sensor 550 (as shown in the link 551 assemblywith solid lines and indicated by numeral 555). In the configuration555, the link 551 rests against the stop 558. In this configuration, thelink 551 assembly is held against the stop 558 by the spring element 556(shown with solid lines), which is preloaded in tension. The springelement 556 is attached to the base structure 205 of the sensor at thehinge joint 557 on one end and to link 551 on the other end. In itsproof mass disengaged configuration, the link 551 assembly is shown inFIG. 12 with dashed lines. In this configuration, the link 551 restsagainst the stop 554. In this configuration, the link 551 assembly isalso held against the stop 554 by the spring element 556 (shown withdotted lines), which is preloaded in tension. A mass element 559 is alsoattached to the link 551 by the extension element 560 as shown in FIG.12. The extension element 560 is long enough so that the mass element559 is positioned to the left of the hinge joint 552 in bothaforementioned configurations of the link 551 assembly shown in solidand dashed lines in FIG. 12.

It is noted that the link 551 and the tension preloaded spring element556 assembly together with the stops 554 and 558 form a toggle mechanismin which the link 551 is in its stable configuration at two differentangular positions, in this case, the two angular positions illustratedby solid and dashed lines, as resting and being held against the stops558 and 554. It is appreciated by those skilled in the art that the link551 assembly together with the stops 554 and 558 form a toggle mechanismsince the spring element 556 is positioned on either side of the lineconnecting the hinge joints 552 and 557 (shown by the centerline 561),thereby applying a clockwise torque to the link 551 when the link is inits right hand configuration (shown with dashed lines), thereby holdingit against the stop 554. However, when the link 551 is in its left handconfiguration (shown with solid lines), the spring element 556 applies acounter-clockwise torque to the link 551, thereby holding it against thestop 558.

The inertia sensor 550 can now be employed for operation in theaforementioned third operational scenario. Consider the situation inwhich the link 551 assembly is in its disengaged configuration (shown indashed lines in FIG. 12). Now if the sensor 550 is oriented such thatthe firing setback acceleration is directed in the direction of thearrow 562, the acceleration will act on the inertia of the mass element559, and apply a counter-clockwise torque to the link 551 assembly, androtate it in the counter-clockwise direction to its configuration 555,thereby allowing the u-shaped locking member 219 to similarly capturethe edge 214 of the plate 211 when it is to be essentially locked to thebase structure 205 of the sensor 550. Then when the sensor 550 issubjected to set-forward acceleration, i.e., when the sensor isaccelerated in the direction of the arrow 563, the acceleration will acton the inertia of the mass element 559, and apply a clockwise torque tothe link 551 assembly, and rotate it in the clockwise direction to itsconfiguration shown with dotted lines, thereby disengaging the u-shapedlocking member 219 from the edge 214 of the plate 211, thereby unlockingthe proof mass 212 and the other moving parts of the sensor from thebase structure 205 of the sensor 550.

It is appreciated by those skilled in the art that by the togglemechanism shown in the embodiment of FIG. 12 may be designed such thatthe acceleration thresholds at which the link 551 assembly is rotatedfrom one of its configurations to the other be different. They can, forexample be achieved by proper positioning of the mass element 559 or byproper positioning of the stops 554 and 558 or proper design of thespring element 556 and its positioning.

It is also appreciated by those skilled in the art that a number of thedisclosed embodiments can also protect the proof mass (inertia element)and other moving parts of inertia sensors when the sensor is subjectedto certain rotational acceleration levels that are beyond predeterminedthreshold. For example, if the sensor embodiments 200 of FIGS. 2 a and250 of FIG. 3 a are rotationally accelerated in the clockwise orcounter-clockwise direction (along an axis perpendicular to the paper),the applied rotational acceleration acts on the inertia of the masselement 207 (assuming all other moving elements, including the link 204assembly has a balanced inertia about the axis of rotation of the hingejoint 206), and pushes the mass element 207 either up or down, and causethe link 204 to rotate counter-clockwise and engage the locking member219 with the tip 214 of the plate 211 to essentially lock the proof mass212 to the base structure 205 of the sensor. The embodiment 300 of FIG.4 a, embodiment 400 of FIG. 6 a, embodiment 450 of FIG. 7 a, embodiment430 of FIG. 8, and embodiment 480 of FIG. 9 would similarly react tohigh clockwise and counter-clockwise accelerations of the respectivesensors and essentially lock the proof mass (inertia element) and othermoving parts of the sensor to its base structure.

It is noted that in the embodiments 300 and 350 of FIGS. 4 a and 5 a,the sliding joints for the locking members 301 and 351 and the member358 of the embodiment 350 of FIG. 5 a are shown to be formed usingrolling elements. In practice, however, particularly when using MEMStechnology to design such inertia based sensors, the sliding joints canbe produced as living joints. The tip of the rotating links (311, 312,454 etc.) may be shaped and positioned relative to the surface of thev-shaped feature (the surface of which may be formed) such that theresulting motion during high acceleration levels is smooth and also thatpossibly, for small accelerations, no movement of the v-shaped elementresults (possibly corresponding to the acceleration thresholds).

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

1. A sensor comprising: a base; at least one component which movesrelative to the base; and one or more locking mechanisms for locking theat least one component in a predetermined stationary position inresponse to external stimuli exceeding predetermined thresholds in atleast first and second directions, where the first direction isdifferent from the second direction.
 2. The sensor of claim 1, whereinthe sensor is selected from a group consisting of an accelerometer andan inertial gyro.
 3. The sensor of claim 2, wherein the external stimuliare first and second accelerations of the sensor, the first accelerationbeing a setback acceleration in the first direction and the secondacceleration being a set forward acceleration in the second direction.4. The sensor of claim 1, wherein the at least one component is a proofmass mounted to a deformable member.
 5. The sensor of claim 1, whereinthe one or more locking mechanisms comprise a first sub-mechanism forlocking the at least one component in the predetermined stationaryposition in response to the external stimuli exceeding a firstpredetermined threshold in the first direction and a secondsub-mechanism for locking the at least one component in thepredetermined stationary position in response to the external stimulusexceeding a second predetermined threshold in the second direction. 6.The sensor of claim 1, wherein the one or more locking mechanismscomprise a single mechanism for locking the at least one component inthe predetermined stationary position in response to the externalstimuli exceeding the predetermined thresholds in both the first andsecond directions.
 7. The sensor of claim 1, wherein the one or morelocking mechanisms engage the at least one component in rotation to lockthe at least one component in the predetermined stationary position. 8.The sensor of claim 1, wherein the one or more locking mechanisms engagethe at least one component in translation to lock the at least onecomponent in the predetermined stationary position.
 9. The sensor ofclaim 1, wherein the one or more locking mechanisms is a first lockingmechanism and the sensor further comprises a second locking mechanismfor one of locking or unlocking the first locking mechanism upon theoccurrence of a predetermined external stimulus.
 10. The sensor of claim1, wherein at least one of the external stimuli is a rotationalacceleration.
 11. A sensor comprising: a base; at least one componentwhich moves relative to the base; and one or more locking means forlocking the at least one component in a predetermined stationaryposition in response to external stimuli exceeding predeterminedthresholds in at least first and second directions, where the firstdirection is different from the second direction.
 12. A method forpassively hardening a sensor from external stimuli greater thanpredetermined thresholds, the method comprising: protecting one or moreof a moving part and mechanism of the sensor from a first externalstimulus in a first direction or minimizing residual vibration of theone or more moving part and mechanism from the first stimulus in thefirst direction; and protecting the one or more of a moving part andmechanism of the sensor from a second external stimulus in a seconddirection or minimizing residual vibration of the one or more movingpart and mechanism from the second stimulus in the second direction;wherein one or more of the first and second stimuli or first and seconddirections are different.
 13. The method of claim 12, wherein theprotecting steps comprise one or more of locking the one or more of themoving part and mechanism to a base structure of the sensor orminimizing elastic deformation of the moving part and mechanism.
 14. Themethod of claim 12, wherein the external stimuli are acceleration of thesensor and the first stimulus is a setback acceleration in the firstdirection and the second stimulus is a set forward acceleration in thesecond direction.
 15. The method of claim 12, wherein the protectingsteps are carried out by separate mechanisms.
 16. The method of claim15, wherein one or more of the separate mechanisms engage the movingpart or mechanism in rotation to lock the moving part or mechanism in apredetermined stationary position.
 17. The method of claim 15, whereinthe one or more of the separate mechanisms engage the moving part ormechanism in translation to lock the moving part or mechanism in apredetermined stationary position.
 18. The method of claim 12, whereinthe protecting steps are carried out by a same mechanism.
 19. The methodof claim 18, wherein the same mechanism engages the moving part ormechanism in rotation to lock the moving part or mechanism in apredetermined stationary position.
 20. The method of claim 18, whereinthe same mechanism engages the moving part or mechanism in translationto lock the moving part or mechanism in a predetermined stationaryposition.
 21. The method of claim 12, wherein the protecting steps arecarried out by one or more first mechanisms and the method furthercomprises providing a second locking mechanism for one of locking orunlocking the one or more of the first locking mechanisms upon theoccurrence of a predetermined external stimulus.
 22. The method of claim12, wherein at least one of the first external stimulus and secondexternal stimulus is a rotational acceleration.